Executive Summary

CVE-2026-13577 exposes Dancer2 (Perl) versions <2.2.0 to insecure session ID generation when Math::Random::ISAAC::XS and Crypt::URandom are missing. The framework falls back to a SHA‑1 hash of low‑entropy data (built‑in rand, file path, counter, PID, memory address, shuffled string), all seeded with a 32‑bit rand. This predictable ID allows session fixation or hijacking, enabling attackers to impersonate users or gain unauthorized access. Mitigation: upgrade to Dancer2 2.2.0 or install the required CSPRNG modules to enforce cryptographically secure session IDs.

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Authoritative CVE Metadata - CVSS Base Score: 8.2 (HIGH) - Published: 2026-07-20T08:16:28.987 - Last Modified: 2026-09-20T11:16:56.817

Original Description: Dancer2 versions before 2.2.0 for Perl generate insecure session ids when required CSPRNG modules are unavailable.

Dancer2::Core::Role::SessionFactory::generate_id silently falls back to a built-in rand-derived session id unless both Math::Random::ISAAC::XS and Crypt::URandom are available.

The fallback session id is generated from a SHA-1 hash of a call to the built-in rand function, the absolute path of the Dancer2::Core::Role::SessionFactory module, an internal counter, the process id, the module instance memory address, and a shuffled string of characters (using the List::Util::shuffle function, which also uses the built-in rand function).

These are all low-entropy and easily guessed sources.

The built-in rand() function is seeded with 32-bits and considered unsuitable for security applications.

Predictable session ids could allow an attacker to gain access to systems.

"We are all inclined to judge ourselves by our ideals; others, by their acts."

— Harold Nicolson